KR20220056334A - Electrolyte for lithium secondary battery and lithium secondary battery comprising thereof - Google Patents

Abstract

The present invention relates to an electrolyte for a lithium secondary battery including a non-aqueous organic solvent containing a certain range of ethyl propionate and propyl propionate, and a lithium secondary battery including the same. The electrolyte for a lithium secondary battery of the present invention reduces the risk of ignition, thereby increasing the safety of a battery.

Description

Electrolyte for lithium secondary battery and lithium secondary battery including same

The present invention relates to an electrolyte for a lithium secondary battery and a lithium secondary battery including the same.

Recently, with the rapid development of electronic devices and electric vehicles, the demand for secondary batteries is increasing. In particular, with the trend of miniaturization and weight reduction of portable electronic devices, a lot of research on lithium secondary batteries with high voltage, high capacity, and high output characteristics is in progress. It has also been commercialized and widely used.

A lithium secondary battery uses a material capable of intercalation and deintercalation of lithium ions as a positive electrode and a negative electrode, and an electrode assembly including a separator interposed between the positive electrode and the negative electrode has a laminated or wound structure, The electrode assembly is built into a battery case and is manufactured by injecting a liquid electrolyte therein. A lithium secondary battery generates electrical energy by oxidation and reduction reactions when lithium ions are inserted and desorbed from the positive and negative electrodes.

However, such a lithium secondary battery has a risk of ignition and explosion due to nail penetration, overcharging, high temperature exposure, external short circuit, local damage, and the like. In particular, in a lithium secondary battery in a charged state, the positive electrode or negative electrode and the electrolyte react with each other at high temperature to generate great heat of reaction, so that a chain exothermic reaction caused by heat causes a safety problem of the battery.

Specifically, since the lithium secondary battery uses an electrolyte made of a flammable non-aqueous organic solvent, when an impact is applied to the battery or an internal short-circuit failure (nail test) through which a needle-like object such as a nail penetrates, the battery interior As the electrochemical energy of the battery is converted into thermal energy, rapid heat generation occurs, and the chemical reaction between the anode or the cathode and the electrolyte is promoted by thermal runaway resulting in a rapid exothermic reaction, which causes the battery to ignite and explode. A problem arises.

In addition, when the battery is overcharged, excess lithium is released from the positive electrode and lithium is inserted into the negative electrode, and lithium metal with high reactivity is deposited on the surface of the negative electrode, resulting in a thermally unstable state, which is a decomposition reaction of the non-aqueous organic solvent contained in the electrolyte. safety problems such as ignition and explosion of the battery due to its rapid exothermic reaction.

In addition, when the battery is exposed to a high temperature for an appropriate time while heating at a constant speed in an oven capable of convection, the active material included in the electrode exotherms and decomposes, and an exothermic reaction due to the reaction of the electrolyte and the active material proceeds inside the battery Thermal runaway due to the local temperature increase in the

Therefore, an essential consideration in the development of a lithium secondary battery is to secure safety, and various technologies have been proposed.

For example, the electrolyte contains additives, such as phosphate esters having self-extinguishing properties, phosphate ester compounds substituted with halogen atoms having self-extinguishing properties, or a radical trapping material. Techniques for improving safety and the like are disclosed. In addition, techniques for increasing the flash point and ensuring safety by using a fluorine-substituted compound or a chlorine-substituted compound as the electrolyte itself have been proposed.

However, when a material having self-extinguishing properties or a material having a high flash point is added to the electrolyte as described above, the effect is not sufficient, the ionic conductivity of the electrolyte is lowered, and the high-rate discharge characteristics or low-temperature characteristics of the battery are lowered. .

Therefore, there is still a need to develop a lithium secondary battery capable of improving battery safety by minimizing ignition and explosion phenomena without degrading battery performance.

Republic of Korea Patent Publication No. 2020-0104904 (2020.09.04), electrolyte, electrochemical device, lithium ion secondary battery and module Republic of Korea Patent No. 10-1252869 (2013.04.03), battery pack exhibiting excellent safety Republic of Korea Patent Registration No. 10-0799866 (Jan. 24, 2008), secondary battery with excellent safety

Accordingly, the present inventors have conducted multifaceted research to solve the above problem, and as a result, when ethyl propionate and propyl propionate are included in a certain content range as non-aqueous organic solvents in the electrolyte for lithium secondary batteries, ignition and explosion are prevented. The present invention was completed by confirming that the safety of the battery could be improved.

Accordingly, an object of the present invention is to provide an electrolyte for a lithium secondary battery capable of implementing excellent safety.

Another object of the present invention is to provide a lithium secondary battery including the electrolyte.

In order to achieve the above object, the present invention provides a non-aqueous organic solvent comprising ethyl propionate and propyl propionate; lithium salt; and an additive, wherein the ethyl propionate is included in an amount of more than 20% by weight based on 100% by weight of the non-aqueous organic solvent.

In one embodiment of the present invention, the propyl propionate is included in an amount of 50 wt% or less based on 100 wt% of the non-aqueous organic solvent.

In one embodiment of the present invention, the ethyl propionate is included in an amount of more than 20% by weight and not more than 25% by weight based on 100% by weight of the non-aqueous organic solvent.

In one embodiment of the present invention, the propyl propionate is included in an amount of 45 wt% or more and 50 wt% or less based on 100 wt% of the non-aqueous organic solvent.

In one embodiment of the present invention, the non-aqueous organic solvent contains the ethyl propionate and propyl propionate in a weight ratio of 1:0.1 to 1:2.

In one embodiment of the present invention, the non-aqueous organic solvent further comprises at least one selected from the group consisting of ethylene carbonate and propylene carbonate.

In one embodiment of the present invention, the additive is vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, nitrile, propene sultone, lithium oxalyl difluoroborate, and 1,3 and at least one selected from the group consisting of ,6-hexanetricarbonitrile.

In one embodiment of the present invention, the additive is included in an amount of 10 to 25% by weight based on 100% by weight of the electrolyte for a lithium secondary battery.

In one embodiment of the present invention, the additive contains 0 to 5% by weight of vinyl ethylene carbonate, 0 to 10% by weight of 1,3-propane sultone, and fluoroethylene carbonate based on 100% by weight of electrolyte for a lithium secondary battery 0 to 10% by weight, 0 to 10% by weight of nitrile, 0 to 5% by weight of lithium oxalyldifluoroborate, and 0 to 5% by weight of 1,3,6-hexanetricarbonitrile.

In addition, the present invention provides a lithium secondary battery comprising the electrolyte for a lithium secondary battery.

As the electrolyte for a lithium secondary battery according to the present invention contains ethyl propionate and propyl propionate in a certain content range, there is an effect of improving the safety of the battery by reducing the possibility of ignition and explosion.

1 is a graph showing the ignition risk evaluation result of the lithium secondary battery of Example 1 according to Experimental Example 1. Referring to FIG.
FIG. 2 is a graph showing the ignition risk evaluation result of the lithium secondary battery of Example 2 according to Experimental Example 1. FIG.
3 is a graph showing the ignition risk evaluation result of the lithium secondary battery of Comparative Example 1 according to Experimental Example 1. Referring to FIG.
4 is a graph showing the ignition risk evaluation result of the lithium secondary battery of Comparative Example 2 according to Experimental Example 1.

Hereinafter, the present invention will be described in more detail.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. Based on the principle that there is, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

The terms used in the present invention are only used to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In the present invention, terms such as 'comprising' or 'having' are intended to designate that the features, numbers, steps, operations, components, parts, or combinations thereof described in the specification exist, and one or more other features It should be understood that this does not preclude the existence or addition of numbers, steps, operations, components, parts, or combinations thereof.

As technology development and demand for portable electronic devices such as mobile phones, notebook computers, and tablet computers increase, the demand for secondary batteries as an energy source is rapidly increasing. This long and low self-discharge rate lithium secondary battery has been commercialized and widely used.

However, as described above, in the lithium secondary battery, when an internal short circuit occurs due to an internal or external factor, an excessive current flows, and as a result, thermal runaway occurs as the amount of heat is seriously increased, so that an ignition or explosion occurs. The chances are significantly increased.

In addition, when the lithium secondary battery is overcharged or exposed to high temperature, heat is generated as the electrolyte is decomposed or the reaction between the electrolyte and the electrode is promoted, which further increases the temperature of the battery, which in turn causes the reaction between the electrolyte and the electrode A thermal runaway phenomenon in which the temperature of the battery rapidly rises by accelerating it occurs, and the battery may ignite or explode.

In particular, since it exhibits high energy density and high voltage, and is highly likely to generate internal heat when the size of the lithium secondary battery is reduced, various methods for solving the safety problem have been proposed.

For example, a physical method of introducing a device using a change in temperature or voltage inside the battery into the battery or a different structure of the battery or a chemical method of adding a material for improving battery safety to an electrode or electrolyte are known.

However, when using the physical method, there is a limitation on applicable batteries, and there is a disadvantage in that it cannot function properly when a fast response time is required, such as an internal short circuit, needle penetration, and local damage. On the other hand, when the chemical method is used, there is a problem in that the performance of the battery is deteriorated due to the added material.

Therefore, in the present invention, including the composition used in the existing electrolyte, but using two specific compounds as a non-aqueous organic solvent, and by optimizing their content, ignition or explosion can be prevented, thereby improving the safety of lithium secondary batteries. An electrolyte for a lithium secondary battery is provided.

Specifically, the electrolyte for a lithium secondary battery according to the present invention includes a non-aqueous organic solvent containing ethyl propionate and propyl propionate; lithium salt; and an additive, wherein the ethyl propionate is included in an amount of more than 20% by weight based on 100% by weight of the non-aqueous organic solvent.

In the present invention, the non-aqueous organic solvent includes ethyl propionate (EP) and propyl propionate (PP).

The non-aqueous solvent is a medium in which ions involved in the electrochemical reaction of the lithium secondary battery move, and includes a combination of ethyl propionate and propyl propionate, and contains 100 weight of the ethyl propionate as a non-aqueous organic solvent By including more than 20% by weight based on %, it is possible to reduce the possibility of ignition or explosion, thereby improving the safety of a lithium secondary battery including the same.

The ethyl propionate may be included in an amount of more than 20% by weight based on 100% by weight of the non-aqueous organic solvent. Specifically, the content of ethyl propionate is based on 100 wt% of the non-aqueous organic solvent, and the lower limit is more than 20 wt%, 21 wt% or more, 21.5 wt% or more, 22 wt% or more, 22.5 wt% or more, or 23 weight % or more, and the upper limit may be 25 wt% or less, 24.5 wt% or less, 24 wt% or less, or 23.5 wt% or less. The content of the ethyl propionate may be set by a combination of the lower limit and the upper limit. When the content of the ethyl propionate is less than the lower limit, the performance of the battery may be deteriorated. Conversely, when the content of ethyl propionate exceeds the upper limit, there may be a problem in that the risk of ignition increases.

The electrolyte for a lithium secondary battery according to the present invention includes propyl propionate in addition to ethyl propionate as described above as a non-aqueous solvent.

The propyl propionate may be included in an amount of 50 wt% or less based on 100 wt% of the non-aqueous organic solvent. Specifically, the content of propyl propionate may be, based on 100% by weight of the non-aqueous organic solvent, the lower limit of 45% by weight or more, 45.5% by weight or more, 46% by weight or more, 46.5% by weight or more, or 47% by weight or more. and the upper limit may be 50 wt% or less, 49.5 wt% or less, 49 wt% or less, 48.5 wt% or less, or 48 wt% or less. The content of the propyl propionate may be set by a combination of the lower limit and the upper limit. When the content of the propyl propionate is less than the lower limit, the performance of the battery may be lowered.

The non-aqueous organic solvent contains the ethyl propionate and propyl propionate in a weight ratio of 1:0.1 to 1:2, preferably 1:1 to 1:2, more preferably 1:1.5 to 1:2 ( ethyl propionate:propyl propionate). When the weight ratio is out of the range, the effect of improving the safety of the battery cannot be secured.

In addition, the non-aqueous organic solvent contains the ethyl propionate and propyl propionate in a ratio of 8:1 to 1:3, preferably 2:3 to 1:3, more preferably 1:2.3 to 1:3. It may be included in a volume ratio (ethyl propionate: propyl propionate). If the volume ratio is out of the range, the risk of ignition may increase, and thus the safety improvement effect of the battery may not be obtained.

The non-aqueous organic solvent may further include an organic solvent commonly used in electrolytes for lithium secondary batteries in addition to the above-described ethyl propionate and propyl propionate.

For example, it may further include at least one selected from the group consisting of a cyclic ether compound, an ester compound, an amide compound, a linear carbonate compound, and a cyclic carbonate compound.

Examples of the cyclic ether compound include 1,3-dioxolane, 4,5-dimethyl-dioxolane, 4,5-diethyl-dioxolane, 4-methyl-1,3-dioxolane, 4-ethyl-1,3 -dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, 2,5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1,3- Dioxolane, 2-vinyl-1,3-dioxolane, 2,2-dimethyl-1,3-dioxolane, 2-methoxy-1,3-dioxolane, 2-ethyl-2-methyl-1,3 -Dioxolane, tetrahydropyran, 1,4-dioxane, 1,2-dimethoxy benzene, 1,3-dimethoxy benzene, 1,4-dimethoxy benzene and isosorbide dimethyl ether It may include one or more selected from the group consisting of, but is not limited thereto.

The ester compound may be selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone and ε-caprolactone. One or more selected types may be used, but the present invention is not limited thereto.

The linear carbonate compound may include at least one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, and ethylpropyl carbonate, but is not limited thereto.

Examples of the cyclic carbonate compound include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene It may include one or more selected from the group consisting of carbonates and halides thereof, but is not limited thereto.

Preferably, the non-aqueous organic solvent may further include at least one selected from the group consisting of ethylene carbonate and propylene carbonate together with ethyl propionate and propyl propionate described above.

When the non-aqueous organic solvent further comprises the ethylene carbonate, the ethylene carbonate is 10 to 25 wt %, preferably 15 to 25 wt %, more preferably 15 to 25 wt %, based on 100 wt % of the non-aqueous organic solvent 20% by weight. When the content of the ethylene carbonate is out of the above range, a problem of deterioration of battery performance may occur.

When the non-aqueous organic solvent further comprises the propylene carbonate, the propylene carbonate is 5 to 20 wt %, preferably 10 to 20 wt %, more preferably 10 to 20 wt %, based on 100 wt % of the non-aqueous organic solvent 15% by weight. When the content of the ethylene carbonate is out of the above range, the performance of the battery may be deteriorated.

According to an embodiment of the present invention, the non-aqueous organic solvent may include ethyl propionate, propyl propionate, ethylene carbonate, and propylene carbonate.

In this case, the non-aqueous organic solvent contains ethyl propionate, propyl propionate, ethylene carbonate, and propylene carbonate in an amount of more than 20 wt% and 25 wt% or less: 45 wt% or more and 50 wt% or less: 15 to 20% by weight: 10 to 15% by weight.

The electrolyte for a lithium secondary battery according to the present invention includes a lithium salt as an electrolyte salt. The type of the lithium salt is not particularly limited in the present invention, and can be used without limitation as long as it can be commonly used in a lithium secondary battery.

For example, as an anion of the lithium salt, F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- ,CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^— , CH ₃ CO ₂ ^— , SCN ^— , and (CF ₃ CF ₂ SO ₂ ) ₂ N ^— may include one or more selected from the group consisting of.

Specifically, as the lithium salt, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAl0 ₄ , LiAlCl ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiN(C ₂ F ₅ SO ₃ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ (Lithium bis(perfluoroethylsulfonyl)imide, BETI), LiN(CF ₃ SO ₂ ) ₂ (Lithium bis(Trifluoromethanesulfonyl)imide, LiTFSI), LiN(C _a F _{2a + 1} SO ₂ )(C _b F _{2b + 1} SO ₂ ) (provided that a and b are natural numbers, preferably 1≤a≤20, and 1≤b≤20), lithium poly[4,4′-(hexafluoro) consisting of loisopropylidene)diphenoxy]sulfonylimide (lithium poly[4,4′-(hexafluoroisopropylidene)diphenoxy]sulfonylimide, LiPHFIPSI), LiCl, LiI, LiB(C ₂ O ₄ ) ₂ , and LiNO ₃ One or more selected from the group may be used. Preferably, the lithium salt may be LiPF ₆ .

The concentration of the lithium salt may be appropriately determined in consideration of ionic conductivity, solubility, and the like, and may be, for example, 0.1 to 4.0 M, preferably 0.5 to 2.0 M. When the concentration of the lithium salt is less than the above range, it is difficult to secure ionic conductivity suitable for driving a battery. Since the performance of the battery may be deteriorated, it is appropriately adjusted within the above range.

The electrolyte for a lithium secondary battery according to the present invention may include additives commonly used in the art for the purpose of improving its function in addition to the above-described composition.

The additive may be used without limitation as long as it can be commonly used in a lithium secondary battery.

For example, the additive is vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1,3-propane sultone (PS), fluoroethylene carbonate ( fluoroethylene carbonate), nitrile, propen sultone (PRS), lithium oxalyl difluoro borate (LiODFB), and 1,3,6-hexanetricarbonitrile (1,3) ,6-Hexanetricarbonitrile; HTCN) may include one or more selected from the group consisting of. Preferably, the additive is 1 selected from the group consisting of vinyl ethylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, nitrile, lithium oxalyldifluoroborate, and 1,3,6-hexanetricarbonitrile It may include more than one species.

The additive may be included in an amount of 10 to 25 wt%, preferably 15 to 20 wt%, based on 100 wt% of the electrolyte for a lithium secondary battery.

Preferably, the electrolyte for a lithium secondary battery according to the present invention is 0 to 5% by weight of vinyl ethylene carbonate, 0 to 10% by weight of 1,3-propane sultone, 0 to 0% by weight of fluoroethylene carbonate, based on 100% by weight of the electrolyte for a lithium secondary battery 10% by weight, 0 to 10% by weight of nitrile, 0 to 5% by weight of lithium oxalyldifluoroborate, and 0 to 5% by weight of 1,3,6-hexanetricarbonitrile may be included as additives.

The electrolyte for a lithium secondary battery of the present invention may further include nitric acid or a nitrite-based compound in addition to the above-described composition.

The nitric acid or nitrite-based compound is not particularly limited in the present invention, but lithium nitrate (LiNO ₃ ), potassium nitrate (KNO ₃ ), cesium nitrate (CsNO ₃ ), barium nitrate (Ba(NO ₃ ) ₂ ), ammonium nitrate inorganic nitric acid or nitrite compounds such as (NH ₄ NO ₃ ), lithium nitrite (LiNO ₂ ), potassium nitrite (KNO ₂ ), cesium nitrite (CsNO ₂ ), and ammonium nitrite (NH ₄ NO ₂ ); Organic nitric acids such as methyl nitrate, dialkyl imidazolium nitrate, guanidine nitrate, imidazolium nitrate, pyridinium nitrate, ethyl nitrite, propyl nitrite, butyl nitrite, pentyl nitrite, and octyl nitrite or a nitrite compound; One selected from the group consisting of organic nitro compounds such as nitromethane, nitropropane, nitrobutane, nitrobenzene, dinitrobenzene, nitropyridine, dinitropyridine, nitrotoluene, dinitrotoluene, and combinations thereof is possible, preferably uses lithium nitrate.

The electrolyte for a lithium secondary battery according to the present invention contains the ethyl propionate and propyl propionate as a non-aqueous organic solvent, and by optimizing the content of the ethyl propionate, the ignition and explosion phenomenon of a lithium secondary battery including the same By preventing this, the safety of the battery can be improved.

In addition, the present invention provides a lithium secondary battery comprising the electrolyte for a lithium secondary battery.

The lithium secondary battery may include a positive electrode; cathode; and an electrolyte interposed therebetween, including the electrolyte for a lithium secondary battery according to the present invention as the electrolyte.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer coated on one or both surfaces of the positive electrode current collector.

The positive electrode current collector is not particularly limited as long as it supports the positive electrode active material and has high conductivity without causing chemical change in the lithium secondary battery. For example, copper, stainless steel, aluminum, nickel, titanium, palladium, fired carbon, a copper or stainless steel surface treated with carbon, nickel, silver, etc., an aluminum-cadmium alloy, etc. may be used.

The positive electrode current collector may form fine irregularities on its surface to enhance bonding strength with the positive electrode active material, and various forms such as films, sheets, foils, meshes, nets, porous bodies, foams, and nonwovens may be used.

The thickness of the positive electrode current collector is not particularly limited, but may be, for example, 3 to 500 μm.

The positive active material layer may include a positive active material and optionally a conductive material and a binder.

The positive active material is not particularly limited as long as it is a material capable of intercalating and deintercalating lithium ions, but may be at least one selected from the group consisting of lithium transition metal oxides and sulfur-based compounds.

As the lithium transition metal oxide, containing two or more transition metals, for example, lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ) and layered compounds substituted with one or more transition metals; Lithium manganese oxide substituted with one or more transition metals, lithium nickel-based oxide, spinel-based lithium nickel-manganese composite oxide, spinel-based lithium manganese oxide in which part of Li in the formula is substituted with alkaline earth metal ion, olivine-based lithium metal phosphate, etc. However, it is not limited thereto.

As the lithium transition metal oxide, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(Ni _a Co _b Mn _c )O ₂ (0 < a < 1, 0 < b < 1, 0 < c < 1 , a+b+c=1), LiNi _{1 -Y} Co _Y O ₂ , LiCo _{1 -Y} Mn _Y O ₂ , LiNi _{1-Y Mn Y} O ₂ (here, 0≤Y<1 ₎ , Li(Ni _a Co _b Mn _c )O ₄ (0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn _{2 - z} Ni _z O ₄ , LiMn _{2 - z} Co _z O ₄ (here, 0<Z<2), Li _x M _y Mn _{2 - y} O _{4 - z} A _z (here, 0.9≤x≤1.2, 0<y<2, 0≤z<0.2, M = at least one of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi, A is -1 or −one or more anions of bivalent), Li _{1 + a} Ni _b M′ _{1- b} O _{2 -c} A′ _c (0≤a≤0.1, 0≤b≤0.8, 0≤c<0.2, M′ is Mn , Co, Mg, Al, etc., is at least one selected from the group consisting of 6-coordinated stable elements, and A' is at least one anion having -1 or -2 valence), LiCoPO ₄ , and LiFePO ₄ 1 type from the group consisting of Those selected above can be used. In addition to these oxides, sulfide, selenide, and halide may also be used.

The sulfur-based compound is inorganic sulfur (S ₈ ), Li ₂ S _n (n≥1), 2,5-dimercapto-1,3,4-thiadiazole (2,5-dimercapto-1,3,4) -thiadiazole), disulfide compounds, such as 1,3,5-trithiocyanuic acid, organosulfur compounds, and carbon-sulfur polymers ((C ₂ S _x ) _n , x= 2.5 to 50, n≥2) may be at least one selected from the group consisting of. Preferably, inorganic sulfur (S ₈ ) may be used.

When the cathode active material is inorganic sulfur, since inorganic sulfur alone does not have electrical conductivity, it may be used in combination with a conductive material such as a carbon material. Accordingly, the positive active material may be a sulfur-carbon composite.

The positive active material may be included in an amount of 40 to 95% by weight, preferably 45 to 90% by weight, more preferably 60 to 90% by weight based on 100% by weight of the positive active material layer constituting the positive electrode. When the content of the positive electrode active material is less than the above range, it is difficult to sufficiently exhibit the electrochemical reaction of the positive electrode. On the contrary, when it exceeds the above range, the content of the conductive material and the binder to be described later is relatively insufficient, and the resistance of the positive electrode increases, There is a problem in that the physical properties of the anode are deteriorated.

The positive electrode active material layer may optionally further include a conductive material for allowing electrons to smoothly move within the positive electrode (specifically, the positive electrode active material) and a binder for well adhering the positive electrode active material to the current collector.

The conductive material electrically connects the electrolyte and the positive electrode active material to serve as a path for electrons to move from the current collector to the positive electrode active material, and may be used without limitation as long as it has conductivity.

For example, the conductive material may include graphite such as natural graphite and artificial graphite; carbon black such as Super-P, Denka Black, Acetylene Black, Ketjen Black, Channel Black, Furnace Black, Lamp Black, and Summer Black; carbon derivatives such as carbon nanotubes and fullerenes; conductive fibers such as carbon fibers and metal fibers; carbon fluoride; A metal powder such as aluminum or nickel powder or a conductive polymer such as polyaniline, polythiophene, polyacetylene, or polypyrrole may be used alone or in combination.

The conductive material may be included in an amount of 1 to 10% by weight, preferably 4 to 7% by weight, based on 100% by weight of the positive active material layer constituting the positive electrode. When the content of the conductive material is less than the above range, electron transfer between the positive active material and the current collector is not easy, and thus the voltage and capacity are reduced. Conversely, if the amount exceeds the above range, the ratio of the positive electrode active material is relatively reduced, and thus the total energy (charge amount) of the battery may decrease. Therefore, it is preferable to determine an appropriate content within the above range.

The binder maintains the positive electrode active material on the positive electrode current collector and organically connects the positive electrode active materials to increase the binding force therebetween, and any binder known in the art may be used.

For example, the binder may include a fluororesin-based binder including polyvinylidene fluoride (PVdF) or polytetrafluoroethylene (PTFE); Styrene-butadiene rubber (styrene butadiene rubber, SBR), acrylonitrile-butydiene rubber, styrene-rubber-based binders including isoprene rubber; Cellulose binders including carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol-based binders; Polyolefin-based binders including polyethylene and polypropylene; polyimide-based binders; polyester-based binders; and a silane-based binder; one selected from the group consisting of, a mixture or copolymer of two or more may be used.

The content of the binder may be 1 to 10% by weight based on 100% by weight of the positive active material layer constituting the positive electrode. If the content of the binder is less than the above range, the physical properties of the positive electrode may be deteriorated, and the positive electrode active material and the conductive material may fall off. It is preferable to determine the appropriate content within the above-mentioned range.

In the present invention, the method for manufacturing the positive electrode is not particularly limited, and a method known by those skilled in the art or various methods for modifying it may be used.

For example, the positive electrode may be prepared by preparing a positive electrode slurry composition including the composition as described above and then applying it to at least one surface of the positive electrode current collector.

The positive electrode slurry composition includes the positive electrode active material, the conductive material, and the binder as described above, and may further include a solvent.

As the solvent, one capable of uniformly dispersing the positive electrode active material, the conductive material, and the binder is used. As the solvent, water is most preferable as an aqueous solvent, and in this case, the water may be distilled water or deionzied water. However, the present invention is not necessarily limited thereto, and if necessary, a lower alcohol that can be easily mixed with water may be used. Examples of the lower alcohol include methanol, ethanol, propanol, isopropanol, and butanol, and preferably, these may be used by mixing with water.

The content of the solvent may be contained at a level having a concentration capable of facilitating coating, and the specific content varies depending on the application method and apparatus.

The positive electrode slurry composition may additionally include, if necessary, a material commonly used in the relevant technical field for the purpose of improving its function. For example, a viscosity modifier, a fluidizing agent, a filler, etc. are mentioned.

The method of applying the positive electrode slurry composition is not particularly limited in the present invention, and for example, a method such as a doctor blade, die casting, comma coating, or screen printing may be used. can be heard In addition, after forming on a separate substrate, the positive electrode slurry may be applied on the positive electrode current collector by pressing or lamination.

After the application, a drying process for removing the solvent may be performed. The drying process is performed at a temperature and time at a level sufficient to remove the solvent, and the conditions may vary depending on the type of the solvent, so the present invention is not particularly limited. As an example, drying by warm air, hot air, low-humidity air, vacuum drying, (far) infrared rays and a drying method by irradiation with an electron beam, etc. are mentioned. The drying rate is usually adjusted to remove the solvent as quickly as possible within a speed range such that the positive electrode active material layer is not cracked or the positive electrode active material layer is not peeled off from the positive electrode current collector due to stress concentration.

Additionally, the density of the positive electrode active material in the positive electrode may be increased by pressing the current collector after drying. Methods, such as a metal mold|die press and roll press, are mentioned as a press method.

The negative electrode may include a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector.

The negative electrode current collector is for supporting the negative electrode active material layer, as described in the positive electrode current collector.

The anode active material layer may include a conductive material, a binder, etc. in addition to the anode active material. In this case, the conductive material and the binder are as described above.

The negative active material may include a material capable of reversibly intercalating or deintercalating lithium ions, a material capable of reversibly forming a lithium-containing compound by reacting with lithium ions, a lithium metal or a lithium alloy.

The material capable of reversibly intercalating or deintercalating lithium ions may be, for example, crystalline carbon, amorphous carbon, or a mixture thereof. The material capable of reversibly forming a lithium-containing compound by reacting with the lithium ions may be, for example, tin oxide, titanium nitrate, or silicon. The lithium alloy is, for example, lithium (Li) and sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr), beryllium (Be), magnesium (Mg), calcium ( Ca), strontium (Sr), barium (Ba), radium (Ra), aluminum (Al), and may be an alloy of a metal selected from the group consisting of tin (Sn).

The method of forming the negative active material is not particularly limited, and a method of forming a layer or a film commonly used in the art may be used. For example, a method such as pressing, coating, or vapor deposition may be used. In addition, a case in which a metal lithium thin film is formed on a metal plate by initial charging after assembling the battery in a state in which there is no lithium thin film in the current collector is also included in the negative electrode of the present invention.

The electrolyte is for causing an electrochemical oxidation or reduction reaction in the positive electrode and the negative electrode through this, as described above.

The injection of the electrolyte may be performed at an appropriate stage during the manufacturing process of the lithium secondary battery according to the manufacturing process and required physical properties of the final product. That is, it may be applied before assembling the lithium secondary battery or in the final stage of assembly.

A separator may be additionally included between the anode and the cathode.

The separator separates or insulates the positive electrode and the negative electrode from each other, and enables lithium ion transport between the positive electrode and the negative electrode, and may be made of a porous non-conductive or insulating material, and is usually used as a separator in a lithium secondary battery. can be used without Such a separator may be an independent member such as a film, or may be a coating layer added to the positive electrode and/or the negative electrode.

As the separator, it is preferable that the electrolyte has low resistance to ion movement and has excellent moisture content to the electrolyte.

The separator may be made of a porous substrate. The porous substrate can be used as long as it is a porous substrate commonly used in secondary batteries, and a porous polymer film can be used alone or by laminating them, for example, a high melting point. A nonwoven fabric made of glass fiber, polyethylene terephthalate fiber, or the like or a polyolefin-based porous membrane may be used, but is not limited thereto.

The material of the porous substrate is not particularly limited in the present invention, and any porous substrate commonly used in electrochemical devices may be used. For example, the porous substrate may include a polyolefin such as polyethylene and polypropylene, a polyester such as polyethyleneterephthalate, a polybutyleneterephthalate, and a polyamide. (polyamide), polyacetal, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide ( polyphenylenesulfide, polyethylenenaphthalate, polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl chloride, polyacrylonitrile, cellulose, nylon (nylon), polyparaphenylene benzobisoxazole (poly(p-phenylene benzobisoxazole) and polyarylate (polyarylate) may include at least one material selected from the group consisting of.

The thickness of the porous substrate is not particularly limited, but may be 1 to 100 μm, preferably 5 to 50 μm. Although the thickness range of the porous substrate is not limited to the above range, when the thickness is excessively thinner than the above-described lower limit, mechanical properties are deteriorated and the separator may be easily damaged during battery use.

The average diameter and pore size of the pores present in the porous substrate are also not particularly limited, but may be 0.001 to 50 μm and 10 to 95%, respectively.

The shape of the lithium secondary battery as described above is not particularly limited, and may be, for example, a jelly-roll type, a stack type, a stack-folding type (including a stack-Z-folding type), or a lamination-stack type.

A lithium secondary battery may be manufactured by sequentially stacking the negative electrode, the separator and the positive electrode, manufacturing an electrode assembly in which electrolyte is injected, putting it in a battery case, and then sealing it with a cap plate and a gasket and assembling it.

At this time, lithium secondary batteries can be classified into various batteries such as lithium-sulfur secondary batteries, lithium-air batteries, and lithium-oxide batteries depending on the material of the anode/cathode used. It can be classified into a bulk type and a thin film type according to the size. Since the structure and manufacturing method of these batteries are well known in the art, a detailed description thereof will be omitted.

In addition, the present invention provides a battery module including the lithium secondary battery as a unit cell.

The battery module may be used as a power source for medium-to-large devices requiring high-temperature stability, long cycle characteristics, and high capacity characteristics.

Examples of the medium-large device include a power tool that is powered by an omniscient motor; electric vehicles, including electric vehicles (EVs), hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and the like; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters (E-scooter); electric golf carts; and a power storage system, but is not limited thereto.

Hereinafter, preferred examples are presented to help the understanding of the present invention, but the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, It goes without saying that such variations and modifications fall within the scope of the appended claims.

Examples and Comparative Examples

[Example 1]

(1) Preparation of electrolyte for lithium secondary battery

LiPF ₆ at a concentration of 1.0 M was dissolved in a non-aqueous organic solvent having a composition of ethyl propionate: propyl propionate: ethylene carbonate: propylene carbonate = 25 wt %: 50 wt %: 15 wt %: 10 wt % to prepare a mixture. prepared.

Based on 100 wt% of the mixture prepared above, 0.5 wt% of vinyl ethylene carbonate, 4 wt% of 1,3-propane sultone, 7 wt% of fluoroethylene carbonate, 2 wt% of nitrile, 0.5 wt% of lithium oxalyldifluoroborate %, and 3 wt% of 1,3,6-hexanetricarbonitrile was added to prepare an electrolyte for a lithium secondary battery.

(2) Lithium secondary battery manufacturing

A cathode slurry composition was prepared by adding 92 wt% of LiCoO ₂ as a cathode active material, 4 wt% of carbon black as a conductive material, and 4 wt% of polyvinylidene fluoride as a binder to N-methyl-2-pyrrolidone (NMP) as a solvent. prepared. The positive electrode slurry composition was applied to an aluminum thin film as a positive electrode current collector having a thickness of about 20 μm, dried to prepare a positive electrode, and then a positive electrode was prepared by roll press.

In addition, artificial graphite as an anode active material, polyvinylidene fluoride as a binder, and carbon black as a conductive material in 96 wt%, 3 wt%, and 1 wt%, respectively, were added to N-methyl-2-pyrrolidone as a solvent. to prepare a negative electrode slurry composition. The negative electrode slurry composition was applied to a 10 μm-thick copper thin film serving as a negative electrode current collector, dried to prepare a negative electrode, and then roll press was performed to prepare a negative electrode.

An electrode assembly was prepared by placing the prepared positive electrode and the negative electrode to face each other, and a porous polyethylene separator having a thickness of 20 μm and a porosity of 45% was interposed therebetween, and the electrode assembly was placed inside the case, and then into the case. A lithium secondary battery was prepared by injecting 16 ml of the electrolyte prepared in (1) above.

[Example 2]

When preparing the electrolyte for a lithium secondary battery, ethyl propionate: propyl propionate: ethylene carbonate: propylene carbonate = 25% by weight: 45% by weight: 20% by weight: Except for using a non-aqueous organic solvent having a composition of 10% by weight was carried out in the same manner as in Example 1.

[Comparative Example 1]

A mixed solution was prepared by dissolving 1.2 M LiPF ₆ in a non-aqueous organic solvent having a composition of propyl propionate: ethylene carbonate: propylene carbonate = 70 wt%: 20 wt%: 10 wt%.

Based on 100 wt% of the mixture prepared above, 0.5 wt% of vinylene carbonate, 3 wt% of 1,3-propane sultone, 3 wt% of FA, 5 wt% of NA, 1 wt% of propene sultone, and lithium oxalyldiol It was carried out in the same manner as in Example 1, except that 0.5 wt% of fluoroborate was added to prepare an electrolyte for a lithium secondary battery.

[Comparative Example 2]

When preparing the electrolyte for a lithium secondary battery, ethyl propionate: propyl propionate: ethylene carbonate: propylene carbonate = 20 wt%: 55 wt%: 15 wt%: Except for using a non-aqueous organic solvent having a composition of 10 wt% was carried out in the same manner as in Example 1.

Experimental Example 1. Evaluation of ignition risk

The batteries prepared in Examples and Comparative Examples were prepared in a fully charged state. Ignition characteristics were evaluated by exposing a fully charged battery at 135 °C for 1 hour after raising the temperature from room temperature to 5 °C per minute (5 °C/min) in an oven capable of convection, and the ignition rate and ignition temperature of the battery.

Specifically, the ignition rate was calculated as a ratio of the number of samples ignited/number of test samples, and the ignition temperature was measured at the ignition point temperature of the ignited sample.

The results obtained at this time are shown in Table 1 and FIGS. 1 to 4 .

Example 1 Example 2 Comparative Example 1 Comparative Example 2 Ignition rate (%) 33 33 100 100 Ignition temperature (℃) 135.59 138.41 135.91 135.95

1 to 4 and Table 1, it can be seen that Examples 1 and 2 have a significantly lower risk of ignition compared to Comparative Examples 1 and 2.

Specifically, it can be seen that the batteries according to Examples 1 and 2 had a lower ignition rate and a higher ignition temperature than the batteries according to Comparative Examples 1 and 2. In particular, the lithium secondary battery of Comparative Example 2, out of the content range of ethyl propionate and propyl propionate presented in the present invention, has a high ignition risk with an ignition rate of 100% despite the ignition temperature being higher than that of Example 1 can be known

From these results, it can be seen that the electrolyte for a lithium secondary battery of the present invention can improve the safety of a lithium secondary battery by preventing ignition and explosion.

Claims (10)

non-aqueous organic solvents including ethyl propionate and propyl propionate;
lithium salt; and
contains additives;
The ethyl propionate is an electrolyte for a lithium secondary battery that is contained in an amount of more than 20% by weight based on 100% by weight of the non-aqueous organic solvent. The method of claim 1,
The propyl propionate is included in an amount of 50% by weight or less based on 100% by weight of the non-aqueous organic solvent, an electrolyte for a lithium secondary battery. The method of claim 1,
The ethyl propionate is included in an amount greater than 20% by weight and not more than 25% by weight based on 100% by weight of the non-aqueous organic solvent, an electrolyte for a lithium secondary battery. The method of claim 1,
The propyl propionate is included in an amount of 45 wt% or more and 50 wt% or less based on 100 wt% of the non-aqueous organic solvent, an electrolyte for a lithium secondary battery. The method of claim 1,
The non-aqueous organic solvent comprises the ethyl propionate and propyl propionate in a weight ratio of 1:0.1 to 1:2, an electrolyte for a lithium secondary battery. The method of claim 1,
The non-aqueous organic solvent further comprises at least one selected from the group consisting of ethylene carbonate and propylene carbonate. The method of claim 1,
The additive is from the group consisting of vinylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, fluoroethylene carbonate, nitrile, propene sultone, lithium oxalyldifluoroborate, and 1,3,6-hexanetricarbonitrile. An electrolyte for a lithium secondary battery comprising at least one selected from. The method of claim 1,
The additive is included in an amount of 10 to 25% by weight based on 100% by weight of the electrolyte for a lithium secondary battery, an electrolyte for a lithium secondary battery. 8. The method of claim 7,
The additive contains 0 to 5% by weight of vinyl ethylene carbonate, 0 to 10% by weight of 1,3-propane sultone, 0 to 10% by weight of fluoroethylene carbonate, and 0% by weight of nitrile based on 100% by weight of electrolyte for a lithium secondary battery to 10% by weight, lithium oxalyldifluoroborate in an amount of 0 to 5% by weight, and 1,3,6-hexanetricarbonitrile in an amount of 0 to 5% by weight, an electrolyte for a lithium secondary battery. anode;
cathode; and
A lithium secondary battery comprising the electrolyte according to claim 1.

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